The amendment would keep Obamacare’s insurance regulations in place — namely requirements that insurers offer 10 essential health benefits, like outpatient care, as well as one that prohibits them from charging the sick more than the healthy.

Under the measure, states could allow insurers to sell plans that don’t meet those ACA standards, as long as they offer at least one qualified health plan.

Cruz, who has said that lowering premiums is his No. 1 goal, told reporters this week that his proposal “expands choices and gives consumers more options, and that’s how you lower prices and that’s how you expand availability of affordable health care.”

Several health care policy experts said the proposal would no doubt cut premiums for people who purchase skimpier plans. But many warned it could lead to far higher costs for people who need the ACA-compliant coverage.

“This type of parallel structure, in practice, undermines the protections for people with pre-existing conditions,” said Matthew Fiedler, a fellow at the Center for Health Policy with the Brooking Institution's Economic Studies Program.

Why? The healthy will flock to the narrower, cheaper products, but the sick will want the ACA-compliant plans, which prevent insurers from charging sick people more than the healthy. Therefore, insurers will raise rates for everyone under those plans, or lose money on those products.

“In practice, sicker people who are not eligible for subsidies will face a choice between a very high premium that’s the same for everybody, or go to this parallel market and have a premium based on health status that is also very high,” Fiedler said.

But Jack Hooper, CEO and co-founder of Take Command Health, a Dallas-based startup that helps individuals and small businesses shop for insurance, said Cruz’s plan has merit, providing certain conditions are in place.

With certain cost controls or a narrower set of health benefits that insurers must cover in all plans, he believes Cruz’s proposal could work. “The way it could go well under Cruz’s plan is if they can prevent a bifurcation of markets or plans, and they can use skimpier, lower-cost plans to bring healthier individuals into the market,” he said.

The problem with Obamacare, he continued, is that despite the individual mandate penalty, not enough young and healthy people have enrolled. But if those Americans can buy an affordable plan that covers, say, five instead of all 10 essential health benefits, “maybe they would, and their dollars would be in the market to help” balance the pool for everyone, Hooper said.

But he acknowledged some of the challenges, telling news outlet Vox that “some market segmentation” could occur but arguing that billions in federal subsidies — which conservatives typically abhor — can help offset those costs for many Americans.

On Thursday, South Dakota Sen. John Thune, a member of Republican leadership, reportedly indicated openness to adding Cruz’s measure with some modifications, according to The Hill.

THUNE says they are open to adding the Cruz amendment on choice if it is changed to prevent risk pool from getting bad

Still, there are signs Cruz’s proposal could run into trouble under Senate parliamentary rules.

Texas Sen. John Cornyn, who monitors vote counts as majority whip, indicated the proposal may not fly under the so-called Byrd rule that governs what is permissible under the reconciliation process the Senate is using to pass the overhaul. Under reconciliation, only spending-related provisions can be considered.

“We’re trying to figure out a way to work it and make that happen,” Cornyn said this week.

Asked if Cruz’s proposal would turn off moderates, Cornyn said the bigger issue for many of those senators is the fate of Medicaid and the opioid epidemic.

“To find consensus, we have to find something acceptable on both of those” issues, Cornyn said.

By Thursday, GOP leaders offered $45 billion in additional dollars to combat the opioid epidemic, according to multiple news reports. Several moderates also are calling for softer Medicaid spending reductions than originally proposed. The nonpartisan Congressional Budget Office predicted the Senate measure would reduce future Medicaid spending by $772 billion over a decade.

GOP leaders also are reportedly mulling retaining Obamacare’s taxes to help lower-income Americans afford health care. Like the House-passed American Health Care Act, the Senate plan has been derided by even some of its own members for appearing to be a tax cut for the wealthy at the expense of the poor.

Cruz’s measure has backing from conservative members in the House and Senate, who view this as their primary ask in ongoing negotiations.

House Freedom Caucus Chairman Mark Meadows, R-N.C., said the proposal could help secure conservative votes in the House if and when the Senate passes its measure and the chambers must negotiate a compromise.

As GOP members work through their differences in a race to dismantle the ACA, Cruz is optimistic that the party, which holds 52 seats in the Senate, will find a way to the 50 votes it needs.

Republicans recognize that “we’re going to have to give some, that we’re going to get less than 100 percent of what we want,” Cruz told reporters this week. “That’s the only way you can bring together a majority.”